Field addressable rewritable media

ABSTRACT

An electrochromic molecular colorant and a plurality of uses as an erasably writeable medium. Multitudinous types of substrates, such as paper, are adaptable for receiving a coating of the colorant. Electrical fringe field or through fields are used to transform targeted pixel molecules between a first, high color state and transparent state, providing information content having resolution and viewability at least equal to hard copy document print. The scope of the invention includes both the liquid coating and the combination of coating on substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 09/919,394 filed on Jul.31, 2001 now U.S. Pat. No. 6,556,470.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO AN APPENDIX

The present application includes a hard copy appendix comprisingpertinent specification pages and drawings of co-inventors' U.S. patentapplication Ser. No. 09/844,862, filed Apr. 27, 2001, by ZHANG et al.for MOLECULAR MECHANICAL DEVICES WITH A BAND GAP CHANGE ACTIVATED BY ANELECTRIC FIELD FOR OPTICAL SWITCHING APPLICATIONS as relates to subjectmatter claimed in accordance with the present invention;

BACKGROUND OF THE INVENTION

1.Field of the Invention

The present invention relates generally to methods and apparatus fordistribution of information, more specifically to electronicallydisplaying informational content and, more particularly to a reusable,high contrast, very high resolution, rewritable print medium and methodsfor fabrication thereof.

2. Description of Related Art

Hard copy and, more recently, electronic display information iscommunicated in many forms and by many means. Erasable-rewritable printmedia communication tools range from simple pencil-on-paper tochalk-on-blackboard to dry marker pen-on-whiteboard. More sophisticatedhard copy processes allow mechanized business and commercial printingprocesses—including laser and ink-jet printers, offset lithography,silkscreen, and the like, for printing—but those processes are usuallyrestricted to the permanent print category (versus “erasable print” or“erasably writable” formats and methods). The bulk of print iscommercially produced and made available through books, magazines,newspapers, and various other forms of permanent ink (“toner” or, moregenerically “colorant”) on cellulose fiber media (commonly known as“paper”). The information content—generally alphanumeric text andgraphical images—contained in this form is of a sufficiently highresolution and contrast to be easily read over prolonged periods of timewithout eye discomfort. Compared to electronic devices, hard copy mediahas the advantages of having zero power consumption while remaininghighly portable, allowing comfortable reading in locations of choice andbody positions that may be periodically varied to change readingdistance and posture to maintain comfort. Such print media, however,requires a relatively high cost in printing, binding, warehousing, anddistribution. The hard copy cost, independent of printing means, isnormally amortized through a single reading, after which the book orother document is physically stored or discarded. Since these lattercost factors also require a definable time expenditure between contentgeneration and availability to the reader, the content of the media isnot contemporaneous; e.g., today's newspaper actually is filled with“what happened yesterday.”

Much print is created by hand, e.g., using pen or pencil on paper. Inmany cases, such print is used for temporary information storage such asphone numbers, reminders, grocery lists, and appointments. Print mediafor such print commonly consists of notepads, Post-It® notes, calendars,tear-sheet display boards, and the like. In each instance, the medium isusually used for its intended purpose then later discarded or ignored,leading to waste, recycling costs, and clutter.

Chalk-on-chalkboard and dry marker pen-on-whiteboard print overcomeissues of media waste and clutter. Such print images are produced withpowders or inks that coat the media surface without permanentattachment, allowing easy image viewing, erasing, and subsequentre-imaging. However, such print is not applicable to portable mediaapplications, such as grocery lists, bound image applications, or otheruses in which the media surface may be smeared by contact. A furtherdisadvantage is the messy residue that results from the removal of thechalk or ink from the media surface.

Business printers, such as the ubiquitous laser and ink-jet printers, inconnection with the Internet overcome some of these problems and providecontemporaneous information distribution with an attendant hard copyprinting availability, but at a higher cost per page and usually at alower quality or in a different format than commercial print. (The termInternet is used herein as a generic term for a collection ofdistributed, interconnected networks (ARPANET, DARPANET, World Wide Web,or the like) that are linked together by a set of industry standardprotocols (e.g., TCP/IP, HTTP, UDP, and the like) to form a generallyglobal, distributed network. (Private and proprietary intranets are alsoknown and are amenable to conforming uses of the present invention.)

Computers, on the other hand, provide virtually instantaneousdistribution of content through the Internet at significantly reducedcost to the reader. Similarly, with the advent of handheld devices suchas palmtop computers, electronic books, net-ready telephones, and“personal digital assistants” (PDAs), print can be generated onelectronic displays of varying sizes and types. Computer displays,however, provide far less comfortable readability by displaying contentat significantly lower resolution than hard copy media. Cathode ray tube(“CRT”) displays have greater resolution capability but have lowportability, if any, and require substantially stationary bodypositioning and reading at a somewhat fixed focal length, leading tocomparatively rapid eye strain and posture discomfort. Liquid crystaldisplays (“LCD”) generally used in portable computers allow somewhatgreater portability, but at the expense of display contrast, off-axisviewability, and higher cost. In part, the lower resolution of portabledisplays stems from the difficulty of matrix addressing at higherresolution.

FIG. 1AA (Prior Art) exemplifies the basic operation of a flat panelelectronic display, such as a commercially available, flat panel, LCD 1(dashed lines are used in this drawing to indicate continuation ofdiscrete elements of the apparatus so as to make the drawing lesscomplicated). Basically, the LCD 1 includes a plurality of pictureelements (“pixels”) defining the resolution of the display, generallyformed by an array of thin film transistors (“TFT”) and too small to beseen in this FIGURE (e.g., 600 dots per inch (“dpi”). A plurality ofgate lines 2 and data lines 3 form a pixel control grid for active area“B” of the panel 1. The gate lines 2 and data lines 3 extend as leads 5outside of the active area B for connection to known manner integratedcircuit drivers. A plurality of pads, one for each line, are formed inregion “C” about the periphery of the active area B as discrete padregions 4 are coupled by the leads 5 to the gate and data lines 2, 3.Color LCD is produced by backlighting the individually switched pixelscrystals through color filters. Note importantly that the resolution ofthe screen is limited by the technology related to interconnectwiring—namely, between the gate and data lines and the microprocessor ormemory sending data—and driver size for each pixel. Moreover, such adevice requires power to maintain each pixel in its current state andcontinually to backlight the crystal screen.

The at least one order of magnitude lower resolution of computerdisplays in comparison to commercial hard copy commonly prevents thereader from seeing a full-page comparable document at one time.Moreover, because of screen size constraints, without a very large videomonitor or shrinking the page to fit a screen, the reader must usemanual controls to scroll the displayed image down the document page inorder to read its entire content. Furthermore, graphic images often cannot fit on a single screen without severe zoom-out reduction in size,limiting the detail which can be displayed. Still further, there is therequirement of booting-up the computing device, turning on the specificapplication (notepad, calendar, or the like), and making at least oneuser command entry to obtain a document page of interest. More oftenthan not, rather than using a PDA to make a note, a simple notescribbled on a piece of paper is much more convenient.

In addition to the aforementioned shortcomings of electronic displays,such displays are relatively high in power consumption, particularly ifthe screen is of the active transistor type. Also, they suffer fromrelatively poor contrast (viewability) in outdoor or other brightambient environment conditions. Emissive displays, such as CRT, plasma,light emitting diode (“LED”), and backlit LCD, have self-illuminatedpicture elements (“pixels”). Emissive displays have excessive powerconsumption by virtue of the need to produce light. Suchself-illumination is still comparatively low in brightness and thereforeappears dark in bright ambient viewing conditions due to the eye'sautomatic adaptation to the ambient brightness. Non-backlit LCDs havepoor contrast under virtually all ambient illumination; the ambientlight reflected from each LCD pixel must pass through polarizers thatsignificantly reduce pixel brightness relative to ambient brightness.This makes the LCD appear dark and of poor contrast. Prior artelectronic displays used in computers and televisions have thereforebeen limited to practical use under controlled office and home ambientillumination. With the advent of mobile computer appliances, such asweb-based telephones, palmtop computers, and televisions, there is agrowing need for display technologies that provide good viewabilityunder the wider range of ambient illumination conditions in which userscommonly communicate, do business and are entertained. Mobile appliancesdemand low power consumption for long battery life. Therefore, there isa growing need for an alternative to conventional electronic displaysthat consume less power.

When a long document is downloaded from the Internet, the reader willcommonly print the contents to gain back the aforementioned hard copymedia benefits. Such printing, however, adds local cost to the processfor documents that commonly are still read just once and eventuallydiscarded. The recycling of paper barely makes a dent in the multiplecosts to the environment. For information distribution, current computersolutions are, thereby, still somewhat antithetical to the needs fordistribution of books, periodicals such as magazines and newspapers, andthe like.

Electrostatically polarized, bichromal particles for displays have beenknown since the early 1960's. The need for an electronic paper-likeprint means has recently prompted development of at least twoelectrochromic picture element (pixel) colorants: (1) amicroencapsulated electrophoretic colorant (see e.g., U.S. Pat. No.6,124,851 (Jacobson) for an ELECTRONIC BOOK WITH MULTIPLE PAGE DISPLAYS,E Ink Corp., assignee), and (2) a field rotatable bichromal colorantsphere (e.g., the Xerox® Gyricon™). Each of these electrochromiccolorants is approximately hemispherically bichromal, where onehemisphere of each microcapsule is made the display background color(e.g., white) while the second hemisphere is made the print or imagecolor (e.g., black or dark blue). The colorants are field translated orrotated so the desired hemisphere color faces the observer at eachpixel. FIGS. 1BB and 1CC schematically depict this type of prior art.

Electronic ink is a recent development. E Ink Corporation (Cambridge,Mass.; www.eink.com) provides an electronic ink in a liquid form thatcan be coated onto a surface. Within the coating are tiny microcapsules(e.g., about 30 μm to 100 μm in diameter, viz. about as thick as a humanhair, thus quite visible to the naked eye). As illustrated in FIG. 1BB(Prior Art), each microcapsule 6 has white particles 7 suspended in adark dye 8. When an electric field is applied and sustained in a firstpolarity, the white particles move to one end of the microcapsule wherethey become visible; this makes the surface appear white at that spot. Acarrier 9 is provided. An opposite polarity electric field pulls theparticles to the other end of the microcapsules where they aresubstantially hidden by the dye; this makes the surface appear dark atthat spot.

The Xerox Gyricon sphere is described in certain patents. FIG. 1CC(Prior Art) is a schematic illustration of this type of sphere. U.S.Pat. No. 4,126,854 (Sheridon '854) describes a bichromal sphere havingcolored hemispheres of differing Zeta potential that allow the spheresto rotate in a dielectric fluid under influence of an addressableelectrical field. U.S. Pat. No. 4,143,103 (Sheridon '103) describes adisplay system using bichromal spheres in a transparent polymericmaterial. U.S. Pat. No. 5,604,027 (Sheridon '027), issued Feb. 18, 1997,for SOME USES OF MICROENCAPSULATION FOR ELECTRIC PAPER, describes aprinter. Essentially, each sphere 10 (again, about 30 μm in diameter)has a bichromal ball 13 having two hemispheres 11, 12, typically oneblack and one white, each having different electrical properties. Eachball is enclosed within a spherical shell 14 and a space 15 between theball and shell is filled with a liquid to form a microsphere so that theball is free to rotate in response to an electrical field. Themicrospheres can be mixed into a substrate which can be formed intosheets or can be applied to a surface. The result is a film which canform an image from an applied and sustained electrical field. Currently,picture element (“pixel”) resolution using this Gyricon spheres islimited to about 100 dpi.

Thus, in the known prior art, each individual colorant device is roughlyhemispherically bichromal; one hemisphere is made the display backgroundcolor (e.g. white) while the second hemisphere is made the print orimage color (e.g. black or dark blue). In accordance with the text andimage data, these microsphere-based colorant devices are fieldtranslated or rotated so the desired hemisphere color faces the observerat each respective pixel. It can be noted that, in commercial practice,displays made from these colorants have relatively poor contrast andcolor. The layer containing the microcapsules is generally at least 3 or4 microcapsules thick. Light that penetrates beyond the layer surfaceinternally reflects off the backside hemispheres causing color (e.g.black and white) intermixing. The image is, for example, thus rendereddark gray against a light gray background. Thus, these technologies donot provide a promising extendability and scaling to high resolutioncolor displays because the colorant switches only between two opaquecolors, disallowing passage of light from different colorant layers fora given pixel. Still further, as is these colorant technologies producea visually poor display resolution relative to hard copy print due tothe relatively large size of the colorant microcapsule spheres.Moreover, the spheres are bichromal, limiting application to two-colorrather than true full color display. Further still, the need foroverlapping spheres in multiple layers to achieve adequate color densitylimits pixel resolution. Yet another limitation is that these coloranttechnologies suffer from poor pixel switching times in comparison tostandard CRT and LCD technology. Each technology relies on theelectrophoretic movement of colorant mass in a dielectric material, suchas isoparafin. The color rotation speed of dichroic spheres underpractical electrical field intensities is in the range of 20milliseconds (ms) or more. At that rate, a 300 dpi resolution printeremploying an electrode array would be limited to under one page perminute print speed. These large sphere colorants require high switchingvoltages (e.g. 80-200 volts) to obtain adequate fields through theconsequently thick (>100 μm) carrier-colorant layer. Such switchingvoltages add high cost to the pixel drive electronics, similar to thatof the high-end matrix LCD apparatus. Thus, those involved in thedevelopment of microcapsule type colorants are struggling with theresolution of these and other related problems rather than focusing on anew molecular level technology as described in accordance with thepresent invention.

There are limitations to microcapsule technologies. The Gyriconmicrocapsule technology produces limited resolution compared to hardcopy due to the relatively large size of the microcapsule spheres,typically a diameter greater than 30 μm. As schematically illustrated inFIG. 1DD (Prior Art), overlapping spheres in multiple layers are neededto achieve adequate color density, limiting pixel resolution to theorder of 300-400 dots-per-inch (“dpi”), whereas, depending on theviewing conditions, the unaided human eye can discriminate to over 1000dpi. Displays made from microcapsules tend to have poor contrast andcolor because light that penetrates beyond the surface layer ofmicrocapsules reflects back off subjacent microcapsules causing colorintermixing. As also demonstrated in FIG. 1DD, poor image contrastarises from backside reflections from each microcapsule. Light enteringand penetrating the interstices of a first layer of microcapsules (nowillustrated as hemispherically colored black and white circles 8) in themedia surface coating 16 reflects and is absorbed by the backside, aswell as front side, hemispheres of subsequent microcapsule layers. Lowcolor density areas of the image become darker and high color densityareas become lighter than would otherwise occur if the microcapsuleswere of uniform color throughout their exterior (as is true withpigments and dyes used in standard printing processes). Thus, in adevice using layers of bichromal microcapsules, the image is oftenactually rendered dark gray against a light gray background

Another limitation to achieving high contrast is that the microcapsulesof the type shown in FIG. 1BB superimposes the two encapsulatedcomponents so that independently of which colorant faces the observer,the second colorant is also visible. Because of the finite nature of thewhite particles 7 and dark color dye 8, when the white hemisphere isdisplayed (rotated toward the viewer), dye will still show in theinterstitial spaces between the white particles; likewise, when the dyehemisphere is displayed, the inherent transparent nature of the dyeallows reflection toward the viewer off the subjacent white particles,lightening the dye color (e.g., deep blue to a medium blue). In otherwords, neither one hundred percent reflection of white nor one hundredpercent of absorption is achieved. Of the type of microcapsule asillustrated in FIG. 1CC, while the hemispheres are opaque black andopaque white, respectively, when light hits the ball 13 it also goesbetween the spheres 10 similarly to as shown in FIG. 1DD, again limitingcontrast and resolution capability.

Furthermore, because they rely upon the electrophoretic movement of amass in a liquid, these microcapsule technologies suffer from poor pixelswitching times in comparison to standard CRT and LCD screens. Colorswitching comprises the relative rotational or translational movement ofsolid particles and liquid from the forward facing to backside facinghemispheres. Relatively slow color switching time is the simple resultof the microcapsule's mass and fluidic drag within the sphere. Thecombined mass and fluidic drag define the time required to affect acolor switch at a given pixel. This, in turn, defines both the switchingenergy requirements and the imaging speed, or “throughput,” of a printerusing media with this technology.

Further still, these relatively large microcapsules require highswitching voltages (e.g., 20-200 volts) to obtain adequate fieldsthrough the relatively thick (greater than 100 μm), multiplemicrocapsule layers 16. Such switching voltages add further cost to thepixel drive electronics, making it comparable to the cost of an LCDscreen.

Still further, these microcapsule technologies do not provide apromising extension to high resolution color displays because thecolorant switches only between two opaque colors, disallowing passage oflight from different colorant subjacent layers for a given pixel. Inother words, microcapsule colorant is not a true dye where outside theparticular dye absorption bandwidth the colorant becomes transparent,allowing different layered chemical compositions to render full colorimages (e.g., as used in color film and print technology). Thus, to gaina full color adaptation, microcapsule colorant based devices will belimited to mosaic patterning which further limits resolution and,ultimately, print quality.

Moreover, the microcapsules themselves suffer from difficultmanufacturing processes and relatively poor durability. Microcapsules,by their nature, have thin walls that are subject to breakage withsubsequent liquid leakage that destroys colorant functionality. Wallthickness is typically of the order of 1-2 μm (or about 10% ofdiameter). Microcapsule breakage may occur by pressure externallyapplied to the media surface, media folding, and by the coating processitself used to make the media. This limits the ability of the displaymedia to be folded or even contacted without a high probability ofcapsule breakage and subsequent loss of imaging function.

It can be concluded that there is not a currently available electronicinformation-displaying mechanism which does not have at least some ofthe foregoing described limitations. More particularly with respect tothe present invention, among the collection of present print and displaystate-of-the-art technologies there does not exist a rewritable mediacapable of commercial hard copy resolution, contrast, and durability.Further, there is not a rewritable media that has the full color qualityappearance nor print readability of commercially printed paper. Thus,there is a need for new and improved print media.

Still further, there is not an electronic rewritable media having goodbright ambient illumination viewability and low power consumption.

Still further in the state-of-the-art, for digital data, mass storagemedia is another form of “rewritable media.” Conventional mass storagemedia includes disks and tapes having a magnetic surface coating. Thesurface coating used in disks and tapes generally contains a thin filmdeposition, or polymer suspension, ferromagnetic crystal layer. Whenexposed to an externally applied magnetic field, the ferromagneticcrystals develop a residual magnetic field that remains stable in theabsence of the external field. The surface coating is written for datastorage by a magnetic writing head translated (by disk revolving or tapestreaming) relative to the surface coating. Data is stored in the formof patterns of residual magnetic fields over the surface. The data isretrieved by a magnetic read head (e.g., an electric coil) translatedrelative to the encoded coating surface, transforming the residualmagnetic field patterns into an oscillating electrical current streamrepresenting the original electronic data form. The area density andfield strength of the magnetically recorded data is determined by thesize of the ferromagnetic crystal domains. In an alternate form, digitaldata is stored on CD-ROM media in the form of a pattern of laser-ablatedor impressed pits on the surface of a light reflective disk. The data isread optically as the disk rotates by reflecting light off the surfaceinto a light sensor. The sensed signal changes as it alternately strikespits and reflective regions between successive pits. The density of datastorage on the disk is a function of the size of the ablated pits andintervening reflective regions. In general, data can be read from aCD-ROM at a significantly greater rate than data can be written, sincewriting requires physical ablation of material in making pits. However,at present, writable CD technology is in its infancy and qualityapparatus is relatively expensive.

With the ever-increasing need to store more data on storage media, thereis increasing need for rewritable storage data storage elements that aremuch smaller than available through conventional magnetic and CD-ROMmedia, creating a higher data density capability. There is also a needto write data at higher data rates.

There is a need for a new technology for the field of displayinginformation that is adaptable to a wide range of implementations.Molecular science holds the promise for solution to many, if not all, ofthe shortcomings of the conventional methods and apparatus currentlyavailable for erasable writing and data storage, retrieval and display.Thus, the present invention provides molecular level solutions, viz.,molecular systems in the form of molecular level optical switches, thatcan be assembled easily to make displays, electronic books, rewritablemedia, electronic lenses, electrically-controlled tinting for windowsand mirrors, optical crossbar switches for fiber optic communications,and much more.

Due to the nature of the present invention which reaches into molecularscience technology, it will become apparent to the reader that therealso arises a question as to what is “print media” and what is a“writing surface” and what is a “display screen” (more simply “display”or “screen” as best fits the context). In some implementations,discriminating as to which conventional definition such an apparatus ormethod of use falls into may be less than clear. Therefore, it should benoted that no limitation on the scope of the present invention isintended by the use of such a particular conventional term whendescribing the details and no such limitation should be impliedtherefrom. Thus, further limitations regarding convention displays isappropriate to understanding the need for and objects and advantages ofthe present invention.

BRIEF SUMMARY OF THE INVENTION

In its basic aspect, the present invention provides a colorant for asubstrate, the colorant including: a molecular system, said systemincluding electrochromic, switchable molecules, each of said moleculesbeing selectively switchable between at least two opticallydistinguishable states, wherein said system is distributable on thesubstrate thereby forming an erasably writable surface. In anotheraspect, the present invention provides a writeable-erasable coating fora substrate, including: a carrier; and within said carrier, acomposition including electrochromic switchable molecules, each of saidmolecules being selectively switchable between at least two opticallydistinguishable states, wherein said molecules are distributable on thesubstrate thereby forming an erasably writable surface. Another aspectof the invention is an erasable writing medium including: a substrate;and at least one layer of a molecular colorant coating affixed to saidsubstrate, wherein molecules of the coating are at least bichromal andselectively switchable between color states under influence of alocalized electric field. Still another aspect of the invention is amethod for writing on electrical field addressable rewritable mediumincluding: providing a substrate having at least one layer of amolecular colorant coating wherein molecules of the coating are at leastbichromal and subjectable to switching between color states underinfluence of a localized electric field and wherein said layer isdistributed across said substrate forming pixels on said medium; andelectrically addressing pixels by selectively controlling each saidlocalized electric field to form document content on said medium.Another aspect of the present invention is a data storage deviceincluding: a substrate; and at least one layer of a molecular colorantcoating wherein molecules of the coating are at least bichromal andsubject to bistable switching between at least two electro-opticalstates under influence of a localized electric field. Still anotheraspect of the present invention is a method of fabricating rewritablemedia including: providing a substrate; and forming with said substrate,a rewritable layer wherein the writable-erasable layer is formed by amolecular system, said system including electrochromic switchablemolecules, each of said molecules being selectively switchable betweenat least two optically distinguishable states.

It is an important advantage and novel feature of the present electronicmedia that rendered images are of a quality as good as or better thanconventional, very high resolution, ink-on-paper and can be rendered asgood as any photographic print.

The foregoing summary is not intended to be an inclusive list of all theaspects, objects, advantages, and features of the present invention norshould any limitation on the scope of the invention be impliedtherefrom. This Summary is provided in accordance with the mandate of 37C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, andmore especially those interested in the particular art, to which theinvention relates, of the nature of the invention in order to be ofassistance in aiding ready understanding of the patent in futuresearches. Objects, features and advantages of the present invention willbecome apparent upon consideration of the following explanation and theaccompanying drawings, in which like reference designations representlike features throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In accordance with 37 C.F.R. 1.84(u), in order to prevent confusion withFIGURES of the Appendix hereto, the drawings of this application usedouble capital letter suffices.

FIG. 1AA (Prior Art) is an elevation view schematic of an LCD screenapparatus.

FIG. 1BB (Prior Art) is an exemplary electronic ink device.

FIG. 1CC (Prior Art) is a schematic depiction of a Xerox Gyricon sphere.

FIG. 1DD is a schematic drawing illustrating the physics associated withthe prior art as illustrated in FIGS. 1BB and 1CC.

FIG. 2AA is a schematic depiction in a magnified, perspective view of aunit of print media in accordance with the present invention.

FIG. 2BB is a magnified detail of FIG. 2AA.

FIG. 3AA is a schematic drawing of a first method and apparatus forwriting-erasing in accordance with the present invention as shown inFIGS. 2AA and 2BB.

FIG. 4AA is a schematic drawing of a second method and apparatus forwriting-erasing in accordance with the present invention as shown inFIGS. 2AA and 2BB.

FIG. 5AA is an alternative embodiment of the present invention asillustrated by FIGS. 2AA-4AA.

FIG. 6AA is an electrical schematic diagram in accordance with thepresent invention.

FIG. 7AA is a schematic drawing illustrating the physics associated withthe present invention as shown in FIGS. 2AA-4AA for comparison to FIG.1DD.

The drawings referred to in this specification should be understood asnot being drawn to scale except if specifically annotated.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made now in detail to a specific embodiment of the presentinvention, which illustrates the best mode presently contemplated by theinventors for practicing the invention. Alternative embodiments are alsobriefly described as applicable. Subtitles are used hereinafter merelyfor the convenience of the reader; no limitation on the scope of theinvention is intended thereby nor should any such limitation be impliedtherefrom.

Definitions

The following terms and ideas are applicable to both the presentdiscussion and the Appendix hereto.

The term “self-assembled” as used herein refers to a system thatnaturally adopts some geometric pattern because of the identity of thecomponents of the system; the system achieves at least a local minimumin its energy by adopting this configuration.

The term “singly configurable” means that a switch can change its stateonly once via an irreversible process such as an oxidation or reductionreaction; such a switch can be the basis of a programmable read-onlymemory (PROM), for example.

The term “reconfigurable” means that a switch can change its statemultiple times via a reversible process such as an oxidation orreduction; in other words, the switch can be opened and closed multipletimes, such as the memory bits in a random access memory (RAM) or acolor pixel in a display.

The term “bistable” as applied to a molecule means a molecule having tworelatively low energy states (local minima) separated by an energy (oractivation) barrier. The molecule may be either irreversibly switchedfrom one state to the other (singly configurable) or reversibly switchedfrom one state to the other (reconfigurable). The term “multi-stable”refers to a molecule with more than two such low energy states, or localminima.

The term “bimodal” for colorant molecules in accordance with the presentinvention may be designed to include the case of no, or low, activationbarrier for fast but volatile switching. In this latter situation,bistability is not required, and the molecule is switched into one stateby the electric field and relaxes back into its original state uponremoval of the field; such molecules are referred to as “bimodal”. Ineffect, these forms of the bimodal colorant molecules are“self-erasing”. In contrast, in bistable colorant molecules the colorantmolecule remains latched in its state upon removal of the field(non-volatile switch), and the presence of the activation barrier inthat case requires application of an opposite field to switch themolecule back to its previous state. Also, “molecular colorant” as usedhereinafter as one term to describe aspects of the present invention isto be distinguished from other chemical formulations, such as dyes,which act on a molecular level; in other words, “molecular colorant”used hereinafter signifies that the colorant molecules as described inthe Appendix and their equivalents are employed in accordance with thepresent invention.

Micron-scale dimensions refers to dimensions that range from 1micrometer to a few micrometers in size.

Sub-micron scale dimensions refers to dimensions that range from 1micrometer down to 0.05 micrometers.

Nanometer scale dimensions refers to dimensions that range from 0.1nanometers to 50 nanometers (0.05 micrometers).

Micron-scale and submicron-scale wires refers to rod or ribbon-shapedconductors or semiconductors with widths or diameters having thedimensions of 0.05 to 10 micrometers, heights that can range from a fewtens of nanometers to a micrometer, and lengths of several micrometersand longer.

“HOMO” is the common chemical acronym for “highest occupied molecularorbital”, while “LUMO” is the common chemical acronym for “lowestunoccupied molecular orbital”. HOMOs and LUMOs are responsible forelectronic conduction in molecules and the energy difference between theHOMO and LUMO and other energetically nearby molecular orbitals isresponsible for the color of the molecule.

An “optical switch,” in the context of the present invention, involveschanges in the electromagnetic properties of the molecules, both withinand outside that detectable by the human eye, e.g., ranging from the farinfra-red (IR) to deep ultraviolet (UV). Optical switching includeschanges in properties such as absorption, reflection, refraction,diffraction, and diffuse scattering of electromagnetic radiation.

The term “transparency” is defined within the visible spectrum to meanthat optically, light passing through the colorant is not impeded oraltered except in the region in which the colorant spectrally absorbs.For example, if the molecular colorant does not absorb in the visiblespectrum, then the colorant will appear to have water cleartransparency.

The term “omni-ambient illumination viewability” is defined herein asthe viewability under any ambient illumination condition to which theeye is responsive.

As a general proposition, “media” in the context of the presentinvention includes any surface, whether portable or fixed, that containsor is layered with a molecular colorant or a coating containingmolecular colorant in accordance with the present invention wherein“bistable” molecules are employed; for example, both a flexible sheetexhibiting all the characteristics of a piece of paper and a writablesurface of an appliance (be it a refrigerator door or a computingappliance using the molecular colorant). “Display” (or “screen”) in thecontext of the present invention includes any apparatus that employs“bimodal” molecules, but not necessarily bistable molecules. Because ofthe blurred line regarding where media type devices ends and displaymechanisms begin, no limitation on the scope of the invention isintended nor should be implied from a designation of any particularembodiment as a “media” or as a “display.”

As will become apparent from reading the Detailed Description andAppendix, “molecule” can be interpreted in accordance with the presentinvention to mean a solitary molecular device, e.g., an optical switch,or, depending on the context, may be a vast array of molecular-leveldevices, e.g., an array of individually addressable, pixel-sized,optical switches, which are in fact linked covalently as a singlemolecule in a self-assembling implementation. Thus, it can be recognizedthat some molecular systems comprise a super-molecule where selectivedomain changes of individual molecular devices forming the system areavailable. The term “molecular system” as used herein refers to bothsolitary molecular devices used systematically, such as in a regulararray pixel pattern, and molecularly linked individual devices. Nolimitation on the scope of the invention is intended by interchangeablyusing these terms nor should any be implied.

General

As illustrated schematically in a magnified partial view in FIG. 2AA,electronic print media 200 in accordance with one embodiment of thepresent invention comprises an electrochromic coating 201 affixedsuperjacently to a backing 202 substrate. The media 200 of the presentinvention employs an electrochromic molecular colorant coating 201 layer(phantom line illustration is used to demonstrate that the layer can infact be transparent as described hereinafter and also to denote that thelayer is very thin, e.g., on the order of a few microns) that containsbistable, electrochromic molecules 203 (represented by greatly magnifieddots) that undergo conformational changes as a result of application ofan electric field that in effect changes selectively localized regionsof this coating from one hue to another. In order to describe theinvention, the electrochromic molecules themselves are depicted assimple dots 203 in FIG. 2BB; however, it should be recognized that thereare literally millions of such molecules (in unlinked system terms) percubic micron of colorant; this can be thought of also as millions ofmolecular optical switching devices per cubic micron of colorant in alinked molecular system.

Optionally, note that as the molecular colorant is spatially addressableat its molecular scale, the colorant molecules may be commingled withmolecules of the substrate. Incorporated substrate coloration andfabrication processes are well known in the print media art.

Bichromal Molecules for Electrochromic Colorants

In order to develop a molecular colorant suitable for rewritable media,what is needed is a molecular system that avoids chemical oxidationand/or reduction, permits reasonably rapid switching from a first stateto a second, is reversible to permit real-time or video ratewriting-erasing applications, and can be adapted for use in a variety ofoptical devices.

The present invention introduces the capability of using molecules foroptical switches, in which the molecules change color when changingstate. This property can be used for a wide variety of write-read-erasedevices or any other application enabled by a material that can changecolor or transform from transparent to colored. The present inventionintroduces several new types of molecular optical property switchingmechanisms: (1) an electric (E) field induced rotation of at least onerotatable section (rotor) of a molecule to change the band gap of themolecule; (2) E-field induced charge separation or re-combination of themolecule via chemical bonding change to change the band gap; (3) E-fieldinduced band gap change via molecule folding or stretching. Thesedevices are generically considered to be electric field devices, and areto be distinguished from electrochemical devices.

The co-pending U.S. patent application, partially incorporated herein asthe Appendix, by Zhang et al. for MOLECULAR MECHANICAL DEVICES WITH ABAND GAP CHANGE ACTIVATED BY AN ELECTRIC FIELD FOR OPTICAL SWITCHINGAPPLICATIONS, supra, describes in detail a plurality of embodiments ofbichromal molecules which can be used in accordance with the presentinvention.

With respect to the technology as described in the Appendix, theoverwhelming advantage of electrochromic molecular colorants overmicrocapsule technology (see, Background of the Invention, supra) forelectronic print media is realization of standardized, conventional hardcopy quality, print contrast, image resolution, switching speed, andcolor transparency. Such use of electrochromic molecular colorants willprovide readable content that resembles conventional printing dyes onpaper forms in color mode, color density, and coating layerincorporability. As depicted in FIG. 7AA, illustrating a stark contrastto the combined absorption-reflection physics of hemisphericmicrocapsule technology as depicted in FIG. 1DD, in the high colordensity state 701 (e.g., black), the electrochromic molecular colorant201 absorbs light uniformly at all light incidence angles and locationsto provide conventional ink color density. In the transparent state 703(FIG. 7AA, right side), the bichromal molecules 203 of the presentinvention do not absorb any visible light appreciably, allowing a mediasubstrate 202 to fully show through the coating layer 201. Thus, to theobserver an electrochromic molecular colorant image appearssubstantially identical to the image as it would appear in conventionalink print on paper. Namely, gradations of the specific high densitycolor, if any, are invisible to the naked eye. The term “electrochromicmolecular colorant” as used herein is expressly intended to include aplurality of different colorant molecules blended to form a layer thatcan achieve a desired composite color other than the exemplary blackstate.

Note additionally, the electrochromic molecular colorant is spatiallyaddressable at its molecular (Angstrom) scale, allowing far greaterimage resolution than the tens-of-microns-scale of microcapsulecolorants. As mentioned above, the molecules may be bistable or bimodal.When bistable, for example in an implementation that appears to be asimple sheet of print media, a variety of printing operation solutionsis available for pixel switching. While for a bistable molecularcolorant in accordance with the present invention a holding E-field viaan addressable matrix of electrodes is not necessary, nonetheless such amatrix may be used (such as for flash writing-erasing the entire sheet,then turning off the E-field to conserve power). For a bimodal, and thusself-erasing, implementation, an electrode array with a holding E-fieldis required. An exemplary, molecular wire adaptable for printing pixelsis described by Kuekes et al. in U.S. Pat. No. 6,128,214 for a MOLECULARWIRE CROSSBAR MEMORY (assigned to the common assignee herein andincorporated herein by reference).

Further, the color switching time for the electrochromic molecularcolorant pervaded pixel regions of the media 200 is significantlyshorter than that for microcapsule colorants, allowing significantlyfaster imaging speeds, in the main because the electrochromic moleculesof the colorant are substantially stationary and change color eitherthrough the movement of electrons, the twisting of molecular elements,or both. In each case, the total mass in movement for any addressedpixel is many orders of magnitude smaller than that required withmicrocapsule colorants; note also that there is additionally no viscousdrag component.

Still further, electronic media 200 containing the electrochromicmolecular colorant coating layer(s) as described in detail hereinafterhave the durability of print on conventional media and are not subjectto colorant breakage through externally applied pressure in manufactureor use as is media coated with microcapsule colorants.

Thus, it is an advantageous feature of the present invention to have acolorant material layer, comprising the bichromal molecules in a form touse as a coating, or film, for adaptable rewritable surfaces. It isanother advantageous feature of the present invention to provide aliquid form of the molecular colorant used to fabricate rewritablemedia, including fixed surfaces.

Electric Field Addressable Rewritable Media Using Bichromal Colorant

Turning now to FIGS. 2AA, 2BB, in a first embodiment the presentinvention comprises an electrical field addressable, rewritable media200 using a bichromal electrochromic molecular colorant. As the colorantis active at a molecular level, it may be formed in a number of ways.Embodiments that are self-assembling, formed using impregnation, or acoating with a liquid, paint, ink, or as an otherwise adapted formliquid vehicle on a substrate 202, are all within the scope of theinvention. The molecular colorant may be a self-assembling system orhave a carrier or vehicle for applying the colorant to a substrate usingconventional deposition and drying (or curing) techniques. The varioustypes of vehicles are discussed in more detail hereinbelow.

The present media 200 invention contemplates a wide variety of substrate202 materials and forms. As merely one example directed toward printerand plain paper-like application uses, the coating 201 may be affixedonto a plastic or other flexible, durable, material substrate 202 in theapproximate size, thickness, and shape of commercial stationery or otherprintable media (see also, U.S. Pat. No. 5,866,284 by Kent D. Vincent,filed on May 28, 1997, for a PRINT METHOD AND APPARATUS FOR RE-WRITABLEMEDIUM; see also U.S. patent application Ser. No. 10/021,446 also byVincent et al.). The particular substrate 202 composition implemented isfully dependent on the specific application and, particularly, to therole that the substrate plays in supporting or creating the electricfield that is imposed across the coating 201 layer. In fact, themolecular coating, at least in a bistable molecular system form, can beused with any surface upon which writing or images can be formed.

The Molecular System Erasably Writable Surface

In a preferred embodiment related to the present invention, a coatinglayer 201 of the media 200 comprises electrochromic molecules 203 (FIGS.2AA-2BB)—self-assembling or molecules in association with anotherchemical component, the “vehicle”—having an electrical field responsivehigh color density state (hereinafter simply “color state”) and atransparent state, or two highly contrasting color states, e.g., a blackstate and a color state (e.g., yellow). The vehicle may include binders,solvents, flow additives, or other common coating additives appropriatefor a given implementation.

Preferably, the colorant of the coating 201 obtains a color state (e.g.,black) when subjected to a first electrical field and a transparentstate when subjected to a second electrical field. The coating 201—ormore specifically, the addressable pixel regions of the media 200—in apreferred embodiment is bistable; in other words, once set or written,the field targeted, “colored pixel,” molecules form the “printedcontent,” remaining in the current printed state until the second fieldis applied, intentionally erasing the image by returning the moleculesto their transparent state at the field targeted pixels. Again, it mustbe recognized that there may be millions of such switched molecule inany given pixel. No holding electrical field is required to maintain theprinted content.

Alternately, the colorant may be monostable, obtaining a localized,first color state (e.g., transparent) when subjected to a localizedelectrical field, then configuratively relaxing to a second color state(e.g., black) in the absence of the field, i.e., bichromal andself-erasing.

Although very different in constitution, the coating composition of thisinvention is analogous to conventional coating formulation technology.The constituents of the colorant will depend on the rheology andadhesion needs of the printing/coating process and substrate material.In some implementations, the colorant strata will be self-assembling.Typically, the coating 201 layer will compose 1%-30% of the solidcontent of the film deposited to form the coating 201 layer on thesubstrate 202. This amount is usually determined by desired image colordensity. The coating 201 may include a polymeric binder to produce adried or cured coating 201 layer on the substrate 202 in which theelectrochromic molecular colorant is suspended. Alternatively, thesolids content may include as much as 100% colorant for certain knownmanner evaporative deposition methods or other thin film depositionmethods wherein the colorant, or an associated vehicle, is deposited. Inthe case of deposition-evaporation methods, there may be no associatedvehicle. In some instances, the colorant must be pre-oriented within thedeposited coating 201 layer to allow an optimum alignment with theelectrical field that will be used to write and erase a printed content.Such orientation may be achieved by solidifying the deposited coating201 layer under the influence of a simultaneously applied electric fieldacross the media 200. In one specific embodiment, the coating 201comprises electrochromic molecular colorant and a liquid, ultravioletlight (“UV”) curable, prepolymer (e.g., (meth)acrylate or vinylmonomers/oligomers). The polymer in this instance is formed in situ onthe media substrate 202 when subjected to ultraviolet radiation. Suchprepolymers are well known in the coatings art.

In a second specific embodiment, coating solidification may occurthrough thermally activated vehicle chemical reaction common to epoxy,urethane, and thermal free radical activated polymerization.

In a third specific embodiment, coating solidification may occur throughpartial or total vehicle evaporation.

The colorant may also self-orient through colorant/coating design thatallows a self-assembled lattice structure, wherein each colorant monomeraligns with adjacent colorant monomers. Such design and latticestructures, for example, are common to dendrimers and crystals.Processes for self-assembly may include sequential monolayer depositionmethods, such as well known Langumir film and gas phase depositiontechniques.

The Substrate

The construction of any specific implementation of the media isdependent upon the writing means, such as are schematically representedin FIGS. 3AA, 4AA, and 5AA, described in more detail hereinafter. Inco-pending applications, the assignee has provided Detailed Descriptionof writing instruments and apparatus for writing using the molecularcolorant. For implementations using an electric field that isperpendicular to the surface of the media (see e.g., FIGS. 4AA and 5AA,the substrate 202 should be fabricated of a material having a dielectricconstant and electrical conductivity which compliments that of thecolorant coating 201 layer. Overall, the substrate may be flexible,semi-flexible, or rigid. It may comprise structures as a film, foil,sheet, fabric, or a more substantial, preformed, three-dimensionalobject. It may be electrically conductive, semi-conductive, orinsulative as appropriate for the particular implementation. Likewise,the substrate may be optically transparent, translucent or opaque, orcolored or uncolored, as appropriate for the particular implementation.Suitable substrate materials for one-side electrode implementations suchas demonstrated by FIG. 3AA may be composed, for example, of paper,plastic, metal, glass, rubber, ceramic, wood, synthetic and organicfibers, and combinations thereof. Suitable flexible sheet materials arepreferably durable for repeated imaging, including for example resinimpregnated papers (e.g. Appleton Papers Master Flex™), synthetic fibersheets (e.g., DuPont™ Tyvex™), plastic films (e.g., DuPont Mylar™,General Electric™ Lexan™, and the like) elastomeric films (e.g.,neoprene rubber, polyurethane, and the like), woven fabrics (e.g.,cotton, rayon, acrylic, glass, metal, ceramic fibers, and the like), andmetal foils. Suitable substrate materials for two-sided electrodeapplications as shown in FIGS. 4AA and 5AA may be composed from the samematerials wherein it is preferable that the substrate be conductive orsemi-conductive, have a conductive layer in near contact with themolecular colorant layer 201, or have a high dielectric constant bulkproperty to minimize voltage drop across the substrate. Conductivesubstrates include metals, highly conjugated conductive polymers, ionicpolymers, salt and carbon filled plastics and elastomers, and the like.Suitable semi-conductive substrates may be composed of conventionaldoped silicon and the like. Substrates with a conductive layer includemetal clad printed circuit board, indium tin oxide coated glass,ceramics, and the like. Vapor deposited or grown semiconductor films onglass, ceramic, metal or other substrate material may also be used. Eachof these substrates are commercially available. High dielectric constantmaterials include metal-oxide ceramics such as titania. Suitablesubstrates may be composed of sintered ceramic forms, woven ceramicfabric, or ceramic filled plastics, elastomers and papers (viaceramic-resin impregnation). Translucent substrates may be used inapplications where ambient illumination and backlit viewing options aremade available on the same substrate. In general, it is desirable thatthe translucent substrate appear relatively opaque white under ambientviewing conditions and transparent white under backlit viewingconditions. Suitable translucent substrates include crystalline andsemi-crystalline plastic, fiber sheets and film (e.g., Dupont Tyvex),matte-surfaced plastic films (e.g., DuPont matte-finish Mylar andGeneral Electric matte-finish Lexan), commercial matte-surfaced glass,and the like.

Apparatus and Methodology

Turning now to FIG. 3AA, for an implementation such as a simple sheet ofrewritable media or a mass data storage media (see Background, supra),or on other bistable molecular colorant coated surfaces where a holdingfield is not used, it is desirable to create an electrical writing fieldfrom a single coating side, for example with an electronic pen tip orelectrode pair 301 and 303, or 301, 305, and to entrain the field acrossthe coating 201 layer. In such instances, an appropriately lowconductivity and dielectric constant colorant coating 201 is desirableto prevent field shunting within the coating layer. The electricalproperties of the substrate 202 are less important with such fringefield (represented by dashed—arrow 307) type writing instruments.

For applications in which it is desirable to create the writing field(dashed—arrow 401) perpendicularly through the media 200 thickness, suchas depicted in FIG. 4AA, with electrodes 403, 405 on opposing sides ofthe media, the substrate 202 preferably has a high dielectric constant,or high electrical conductivity if the adjacent electrode is common toall pixels. These properties minimize the voltage drop (loss) across thesubstrate 202 to minimize media switching voltage requirement. Forexample, employable substrates 202 are represented by the group:titania-filled plastic, certain high dielectric constant resinimpregnated papers, and metals.

For certain implementations, e.g., large easel boards (note thatmolecular colorant based electronic displays and display screens, suchas those used in computers, PDA's and the like are described in otherco-pending applications by Vincent et al. and assigned to the commonassignee herein), it is desirable to coat substrates having an electrodeor array of electrodes included on the substrate surface to be coated.Representative substrates include metal-clad fiberboards, printedcircuit boards, metalized glass, surface etched metalized glass,graphite impregnated rubbers and plastics, sheet metals, and the like.

Turning now to FIG. 5AA, in a more costly embodiment, the media 200′ mayinclude a substrate 202 having a reflective substrate 501 coated with apreferred background color layer 503, wherein the background colorremains fixed and independent of the imposed electric writing fields(dashed—arrow 505). This surface 501 will normally create the backgroundcolor of the media 200′ when the molecular colorant coating 201 layer isswitched to the transparent state. Such surface coatings generallycomprise a conventional pigment or colorant incorporated in a polymerbinder. As with the substrate 202, the surface 501 coating 503 comprisesa binder and colorant of a composition chosen to maintain the integrityof the electric field 505 imposed on the media 200′ and to minimizeadditional voltage drop across the media. Alternatively, a conventionalpigment or colorant may be incorporated in the substrate 202 itself.Such surface coating and incorporated substrate coloration fabricationprocesses are well known in the media art.

The media 200′ of the present invention may further include a protectivesurface 507 layer. In general, the protective surface layer 507 isvisibly transparent and protects the colorant coating 201 from abrasion,photo-oxidative color fade, chemical decomposition, or otherenvironmentally imposed factors that may alter the integrity of themedia 200′. The protective surface layer 507 fabrication can be in aknown manner, such as a polymeric coating, a transparent materialdeposition, or a laminate. As examples, polymethyl methacrylate andpolyurethane type polymeric coatings are known to contain ultravioletradiation absorbing additives; thin film, vapor deposited, glass; andpolymer laminate films may be employed. Methods of layer application arealso well known in the art. As with the substrate 202, the protectivesurface layer 507 is preferably composed to maintain the integrity ofthe electric field imposed on the media and to minimize additionalvoltage drop across the media.

The colorant coating 201 of any of the aforementioned media 200, 200′ ofthis invention may comprise a mosaic pattern of alternating colorantmolecule pixel regions that are common to the same coating plane. Suchalternating colors may include, for example, a repeating pattern ofcyan, magenta and yellow pixels. Mosaic patterns for color displays arewell known in the display art and are useful to the present inventionfor producing color images. Achievable resolution is fine enough so thatcontiguous print content regions of a color can be attained in a mannerthat is substantially seamless to the naked eye. A number of printingprocesses are well suited for accurate deposition of each colored pixelin the mosaic. Such processes include: offset lithography, gravure,silkscreen, ink-jet, electrophotography, and photomask deposition.Ink-jet offers a particularly attractive mosaic deposition means fromthe viewpoint of small controlled dot shapes and placement in anon-contact deposition process. For most applications, the pattern ofpixels in the mosaic must coincide with the pattern of electrodesconstructed to drive each pixel. Furthermore, a mosaic pattern may alsobe formed by printing mosaic color pattern as background or by the useof conventional mosaic filters as part of, or adjacent to, a protectivelayer. The present embodiment shows use of black and transparent statemolecules (see, e.g., FIG. 7) which can be used as a layer over apre-printed color mosaic background (e.g., printed conventionally suchas with a CYM ink-jet apparatus). No color shows through in the blackswitch state and color shows through in the transparent switch state.Likewise the use of a conventional color filter (e.g., as used in colorLCD screens) for backlit or projection display use can be implemented;the back-transparent colorant molecules serves as a light valve similarto liquid crystal shutters. The benefit of each of these approaches isthat it uses a single molecular colorant with conventional mosaiccolorant (ink, filters). The color mosaic filter may optionally beprinted as a background layer on an otherwise transparent substrate(e.g., glass). These approaches allow full color without inherent color,switched molecules (e.g., yellow/transparent state, and the like).

Importantly, because the colorant molecules can be implemented in anembodiment having a transparent state, colorant strata can be layered(e.g., molecules switching between transparent and primary colors inseparate strata layers) such that very high resolution, full colorrendering can be accomplished through multi-color layer pixelsuperposition (e.g., overlays of the subtractive primary colors cyan,magenta and, yellow); only in the present invention such implementationswill be in fully rewritable formats. As noted in the Background section,this solves one of the limitations inherent in the microcapsuletechnologies.

The thickness and dielectric constant of each coating, layer andsubstrate component comprising the media 200, 200′ of this invention ispreferably selected to accommodate the spacing of opposing electrodes,field geometry, and voltage used to switch a given media pixel. Thepixel resolution, as measured in pixels per linear dimension (e.g., 1200pixels/inch (“ppi”) for color, 4800 ppi for grey scale), is inverselyproportional to the electrode spacing. The pixel switching voltage forthe embodiment as shown in FIG. 5AA is equivalent to the sum of voltagedrops over the respective layers that interpose the opposing electrodes.This is represented by the electrical schematic of FIG. 6AA. Each layerintroduces a series capacitance with a voltage drop, “V_(n),”proportional to the layer thickness (“d_(n)”) and inversely proportionalto the layer dielectric constant (“k_(n)”), where

-   “q”=the electronic charge (Coulombs) accumulated at an electrode,-   “ε”=the permitivity constant, and-   “A”=coating layer surface area subjected to the field.    The substrate 202 generally represents a significant voltage drop    and source for electrical field broadening if included within the    electrode field. Thus, the substrate 202 is preferably a conductive    material, thereby making an effective common ground plane electrode    in applications such as FIGS. 4AA and 5AA that require the substrate    to lie within the writing electric field. Metals and conductive and    ionic polymers are good material choices in such instances.    Alternatively, the substrate 202 may be composed of a high    dielectric material to offset the voltage loss in an embodiment    represented schematically by FIG. 4AA. Titania, or a like high    dielectric filler, impregnated polymers, fiber-based papers, and    plastics may be used for this purpose.

Exemplary Usefulness

Erasably Writeable Media

The electrochromic molecular colorant system in accordance with thepresent invention may be described in part as an electrochromicmolecular colorant allowing incorporation into virtually all types ofinks, paints, coatings, and the like, where conventional colorants arecommonly used. Further, it may be applied to a substrate using most anyof the standard processes in which conventional pigments are used. Thesebenefits are, again, in stark contrast to microcapsule colorants wherethe size and fragile nature of the microcapsules prevents both stableliquid dispersion and subjection to physical forces common to moststandard application processes.

Solutions containing the electrochromic molecular colorant of thepresent invention may be, for example, spray, dip, roller, cast or knifecoated onto large surfaces or webs of material, such as paper or plasticfilms to form the rewritable region of the surfaces or webs. Moreover,the adaptability of the molecular colorant of the present invention tostandard application processing allows virtually any surface—forexample, refrigerator doors, white boards, desktops, wristwatchsurfaces, computer display fascia, or any surface on which note takingmay be desirable—to be coated with the electric field rewritableelectrochromic molecular colorant having the molecular colorant therein.

Using bistable, bichromal molecular colorant, such surfaces then may bewritten and erased with devices capable of producing a selectivelylocalized electric field within the coating. Paper-like sheets, surfacecoated with the electrochromic molecular colorant of the presentinvention, may be imaged with printers capable of producing pixel-sizedelectric fields, for example, through an electrode array. Thesewriting-erasing apparatus, devices, and methods of operation are thesubject of other patent applications by Kent Vincent et al.,Hewlett-Packard, assignee.

Inks or paints containing the present electrochromic molecular colorantmay be selectively printed on various substrates, for example, toproduce rewritable areas on a pre-printed form where the pre-printedareas are printed using non-erasable, conventional ink. Such rewritableareas may be printed with the molecular colorant using conventionaloffset lithography, gravure, intaglio, silkscreen, ink-jet processes, orthe like.

Note that some such erasably writable areas may include backlighting,wherein the electrochromic molecular colorant ink is printed on atransparent substrate for overhead projection use, or may be printed ona white substrate for passive light viewing. In the backlitconfiguration, a mosaic of electrochromic molecular colorant pixels maybe used as an active color filter for projection displays. In thepassive light configuration, the mosaic of electrochromic molecularcolorant pixels may form a stationary print-on-paper-like stationary.The electrochromic molecular colorant requires no passage of current andis, therefore, less subjected to display life reducing processes such asoxidation and charge trapping. Such passive light displays also offerbetter viewing under natural lighting conditions. Generally, theelectrochromic molecular colorant requires far less drive energy thanknown electronic display means since it does not emit light or requirebacklighting. Further energy savings is realized through optionalbi-stable colorant color states. Unlike liquid crystals, the bi-stableelectrochromic molecular colorant does not require a field to hold agiven image.

Data Storage Applications

The present invention electrochromic molecular colorant offerssignificant storage density, cost and write speed benefits overconventional ferromagnetic coating and CD-ROM storage media. The datastorage element in this instance becomes a bi-stable, twoelectro-optical states molecule, or more accurately an approximatemolecule-wide, or larger, column of layered molecules, that is writtenthrough a selectively localized electric field and read optically or byelectric field sensing. Optical reading electrical field sensingapplications are well known in the art. The molecular storage elementprovides significant storage density advantage over the much largermagnetic crystal or laser readable pit storage elements. Theelectrochromic molecular colorant may be incorporated in a polymer resinand inexpensively coated on standard storage media substrates using mostany standard continuous thick film coating method. Thin film depositioncoating methods may also be used. Depending on colorant structure andbi-stability, the bit writing time is expected to range between 10⁻³ and10⁻⁹ seconds (based on computer simulations).

Summary

The present invention provides an electrochromic molecular colorant 201and a plurality of uses as an erasably writeable medium 201.Multitudinous types of substrates, such as paper, 202 are adaptable forreceiving a coating of the colorant. Electrical fringe field 307 orthrough fields 401, 501 are used to transform targeted pixel moleculesbetween a first, high color state 701 and a second, contrasting state ortransparent state 703, providing information content having resolutionand viewability at least equal to hard copy document print.

The foregoing description of the preferred embodiment of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form or to exemplary embodiments disclosed.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. Similarly, any process stepsdescribed might be interchangeable with other steps in order to achievethe same result. The embodiment was chosen and described in order tobest explain the principles of the invention and its best mode practicalapplication, thereby to enable others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use or implementation contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto and their equivalents. Reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather means “one or more.” Moreover, no element, component,nor method step in the present disclosure is intended to be dedicated tothe public regardless of whether the element, component, or method stepis explicitly recited in the following claims. No claim element hereinis to be construed under the provisions of 35 U.S.C. Sec. 112, sixthparagraph, unless the element is expressly recited using the phrase“means for . . . ” and no process step herein is to be construed underthose provisions unless the step or steps are expressly recited usingthe phrase “comprising the step(s) of . . . .”

APPENDIX

Molecules evidencing one of several new types of switching are providedfor the colorant layer 101. That is to say, the present inventionintroduces several new types of switching mechanisms that distinguish itfrom the prior art:

-   -   (1) an electric field (“E-field”) induced rotation of at least        one rotatable section (rotor) or a molecule to change the band        gap of the molecule;    -   (2) E-field induced charge separation or recombination of the        molecule via chemical bonding change to change the band gap; and    -   (3) E-field induced band gap change via molecular folding or        stretching.        Thus, the color switching is the result of an E-field induced        intramolecular change rather than a diffusion or        oxidation/reduction reaction, in contrast to prior art        approaches. Also, the part of the molecule that moves is quite        small, so the switching time is expected to be quite fast. Also,        the molecules are much simpler and thus easier and cheaper to        make than the rotaxanes, catenanes, and related compounds.

The following are examples of model molecules with a brief descriptionof their function:

-   -   (1) E-field induced band gap change via molecular conformation        change (rotor/stator type of model)—FIGS. 4 and 5 a-5 c;    -   (2a) E-field-induced band gap change caused by the change of        extended conjugation via charge separation or recombination        accompanied by increasing or decreasing band localization—FIG. 6        a;    -   (2b) E-field-induced band gap change caused by change of        extended conjugation via charge separation or recombination and        π-bond breaking or formation—FIG. 6 b; and    -   (3) E-field induced band gap change via molecular folding or        stretching.

Each model, with supporting examples, is discussed below. However, theexamples given are not to be considered limiting the invention to thespecific molecular systems illustrated, but rather merely exemplary ofthe above switching mechanisms.

Model (1): E-Field-Induced Band Gap Change via Molecular ConformationChange (Rotor/Stator Type of Model)

FIG. 4 is a schematic depiction of one embodiment of this model, whichinvolves an E-field-induced band gap change via molecular conformationchange (rotorlstator type of model). As shown In FIG. 4, the molecule430 comprises a rotor portion 432 and a stator portion 434. The rotorportion 432 rotates with an applied electric field. In one state,depicted on the left side of the drawing, there is an extendedconjugation through the entire molecule, resulting in a relativelysmaller band gap and thereby longer wavelength (red-shifted)photo-absorption. In the other state, following rotation of the rotor,depicted on the right side of the drawing, the extended conjugation ischanged, resulting in a relatively larger band gap and thereby shorterwavelength (blue-shifted) photo-absorption. FIGS. 5 a-5 c depict analternate, and preferred, embodiment of this Model 1; these latterFigures are discussed in connection with Examples 1 and 2 of this Model1 below.

The following requirements must be met in this model:

(a) The molecule must have at least one rotor segment and at least onestator segment;

(b) In one state of the molecule, there should be delocalized HOMOsand/or LUMOs (π-states and/or non-bonding orbitals) that extend over alarge portion of the molecule (rotor(s) and stator(s)), whereas in theother state, the orbitals are localized on the rotor(s) and stator(s),and other segments;

(c) The connecting unit between rotor and stator can be a single σ-bondor at least one atom with (1) non-bonding electrons (p or otherelectrons), or (2) π-electrons, or (3) π-electrons and non-bondingelectron(s);

(d) The non-bonding electrons, or π-electrons, or π-electrons andnon-bonding electron(s) of the rotor(s) and stator(s) can be localizedor de-localized depending on the conformation of the molecule, while therotor rotates when activated by an E-field;

(e) The conformation(s) of the molecule can be E-field dependent orbi-stable;

(f) The bi-stable state(s) can be achieved by intra- or inter-molecularforces such as hydrogen bonding, Coulomb force, van der Waals force,metal ion complex or dipole inter-stabilization; and

(g) The band gap of the molecule will change depending on the degree ofnon-bonding electron, or π-electron, or π-electron and non-bondingelectron delocalization of the molecule. This will control the opticalproperties (e.g., color and/or index of refraction, etc.) of themolecule.

Following are two examples of this model (Examples 1 and 2):

The novel bi-modal molecules of the present invention are active opticaldevices that can be switched with an external electric field.Preferably, the colorant molecules are bi-stable. The general idea is todesign into the molecules a rotatable middle segment (rotor) 432 thathas a large dipole moment (see Examples 1 and 2) and that links twoother portions of the molecule 430 that are immobilized (stators) 434.Under the influence of an applied electric field, the vector dipolemoment of the rotor 432 will attempt to align parallel to the directionof the external field. However, the molecule 430 is designed such thatthere are inter- and/or intra-molecular forces, such as hydrogen bondingor dipole-dipole interactions as well as steric repulsions, thatstabilize the rotor 432 in particular orientations with respect to thestators 434. Thus, a large electric field is required to cause the rotor432 to unlatch from its initial orientation and rotate with respect tothe stators 434.

Once switched into a particular orientation, the molecule 430 willremain in that orientation until it is switched to a differentorientation, or reconfigured. However, a key component of the moleculedesign is that there is a steric repulsion or hindrance that willprevent the rotor 432 from rotating through a complete 180 degree halfcycle. Instead, the rotation is halted by the steric interaction ofbulky groups on the rotor 432 and stators 434 at an opticallysignificant angle of typically between 10° and 170° from the initialorientation. For the purposes of illustration, this angle is shown as90° in the present application. Furthermore, this switching orientationmay be stabilized by a different set of inter- and/or intra-molecularhydrogen bonds or dipole interactions, and is thus latched in place evenafter the applied field is turned off. For bi- or multi-stable colorantmolecules, this ability to latch the rotor 432 between two statesseparated by an optically significant rotation from the stators iscrucial.

The foregoing strategy may be generalized to design colorant moleculesto provide several switching steps so as to allow multiple states (morethan two) to produce a multi-state (e.g., multi-color) system. Suchmolecules permit the optical properties of the colorant layer to betuned continuously with a decreasing or increasing electric field, orchanged abruptly from one state to another by applying a pulsed field.

Further, the colorant molecules may be designed to include the case ofno, or low, activation barrier for fast but volatile switching. In thislatter situation, bi-stability is not required, and the molecule isswitched into one state by the electric field and relaxes back into itsoriginal state upon removal of the field (“bi-modal”). In effect, theseforms of the bi-modal colorant molecules are “self-erasing”. Incontrast, with bi-stable colorant molecules, the colorant moleculeremains latched in its state upon removal of the field (non-volatileswitch), and the presence of the activation barrier in that caserequires application of an opposite field to switch the molecule back toits previous state.

When the rotor 432 and stators 434 are all co-planar, the molecule isreferred to as “more-conjugated”. Thus, the non-bonding electrons, orπ-electrons, or π-electrons and non-bonding electrons of the colorantmolecule, through its highest occupied molecular orbital (HOMO) andlowest unoccupied molecular orbital (LUMO), are delocalized over a largeportion of the molecule 430. This is referred to as a “a red-shiftedstate” for the molecule, or “optical state I”. In the case where therotor 432 is rotated out of conjugation by approximately 90° withrespect to the stators 434, the conjugation of the molecule 430 isbroken and the HOMO and LUMO are localized over smaller portions of themolecule, referred to as “less-conjugated”. This is a “blue-shiftedstate” of the molecule 430, or “optical state II”. Thus, the colorantmolecule 430 is reversibly switchable between two different opticalstates.

It will be appreciated by those skilled in the art that in the idealcase, when the rotor 432 and stators 434 are completely coplanar, thenthe molecule is fully conjugated, and when the rotor 432 is rotated atan angle of 90° with respect to the stators 434, then the molecule isnon-conjugated. However, due to thermal fluctuations, these ideal statesare not fully realized, and the molecule is thus referred to as being“more-conjugated” in the former case and “less-conjugated” in the lattercase. Further, the terms “red-shifted” and “blue-shifted” are not meantto convey any relationship to hue, but rather the direction in theelectromagnetic energy spectrum of the energy shift of the gap betweenthe HOMO and LUMO states.

Examples 1 and 2 show two different orientations for switching themolecules. Example 1a below depicts a first generic molecular examplefor this Model 1.

where:

The letter A⁻ represents an Acceptor group; it is anelectron-withdrawing group. It may be one of the following: hydrogen,carboxylic acid or its derivatives, sulfuric acid or its derivatives,phosphoric acid or its derivatives, nitro, nitrile, hetero atoms (e.g.,N, O, S, P, F, Cl, Br), or functional groups with at least one ofabove-mentioned hetero atoms (e.g., OH, SH, NH, etc.), hydrocarbons(either saturated or unsaturated) or substituted hydrocarbons.

The letter D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), or substitutedhydrocarbon or functional group with at least one of hetero atom (e.g.,B, Si, I, N, O, S, P). The donor is differentiated from the acceptor bythat fact that it is less electronegative, or more electropositive, thanthe acceptor group on the molecule.

The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

The letters SA and SB are used here to designate Stator A and Stator B.They may be a hydrocarbon (either unsaturated or saturated) orsubstituted hydrocarbon. Typically, these hydrocarbon units containconjugated rings that contribute to the extended conjugation of themolecule when it is in a planar state (red shifted state). In thosestator units, they may contain the bridging group G_(n) and/or thespacing group R_(n). The bridging group (e.g., acetylene, ethylene,amide, imide, imine, azo, etc.) is typically used to connect the statorto the rotor or to connect two or more conjugated rings to achieve adesired chromophore. The connector may alternately comprise a singleatom bridge, such as an ether bridge with an oxygen atom, or a directsigma bond between the rotor and stator. The spacing groups (e.g.,phenyl, isopropyl or tert-butyl, etc.) are used to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing space for each rotor to rotate over the desiredrange of motion.

Example 1b below is a real molecular example of Model 1. In Example 1b,the rotation axis of the rotor is designed to be nearly perpendicular tothe net current-carrying axis of the molecules, whereas in Example 2,the rotation axis is parallel to the orientation axis of the molecule.These designs allow different geometries of molecular films andelectrodes to be used, depending on the desired results.

where:

The letter A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

The letter D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), or substitutedhydrocarbon or functional group with at least one of hetero atom (e.g.,B, Si, I, N, O, S, P). The donor is differentiated from the acceptor bythat fact that it is less electronegative, or more electropositive, thanthe acceptor group on the molecule.

The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g. metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

Letters R₁, R₂, R₃ represent spacing groups built into the molecule. Thefunction of these spacer units is to provide an appropriate3-dimensional scaffolding to allow the molecules to pack together whileproviding rotational space for each rotor. They may be any one of thefollowing: hydrogen, hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

Letters G₁, G₂, G₃, and G₄ are bridging groups. The function of thesebridging groups is to connect the stator and rotor or to connect two ormore conjugated rings to achieve a desired chromophore. They may be anyone of the following: hetero atoms (e.g., N, O, S, P, etc.) orfunctional groups with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbons (either saturated or unsaturated)or substituted hydrocarbons. The connector may alternately comprise asingle atom bridge such as an ether bridge with an oxygen atom, or adirect sigma bond between the rotor and stator.

In Example 1b above, the vertical dotted lines represent other moleculesor solid substrates. The direction of the switching field isperpendicular to the vertical dotted lines. Such a configuration isemployed for electrical switching; for optical switching, the linkingmoieties may be eliminated, and the molecule may be simply placedbetween the two electrodes. They may also be simply used to link onemolecule to another molecule or a molecule to an organic or inorganicsolid substrate.

Referring to FIG. 5 a, the molecule shown above (Example 1b) has beendesigned with the internal rotor 432 perpendicular to the orientationaxis of the entire molecule 430. In this case, the external field isapplied along the orientation axis of the molecule 430 as pictured—theelectrodes (vertical dotted lines) are oriented perpendicular to theplane of the paper and perpendicular to the orientation axis of themolecule 430. Application of an electric field oriented from left toright in the diagrams will cause the rotor 432 as pictured in the upperdiagram to rotate to the position shown on the lower right diagram, andvice versa. In this case, the rotor 432 as pictured in the lower rightdiagram is not coplanar with the rest of the molecule, so this is theblue-shifted optical state of the molecule, whereas the rotor iscoplanar with the rest of the molecule on the upper diagram, so this isthe red-shifted optical state of the molecule. The structure shown inthe lower left diagram depicts the transition state of rotation betweenthe upper diagram (co-planar, conjugated) and the lower right diagram(central portion rotated, non-conjugated).

The molecule depicted in Example 1b is chromatically transparent orblue-shifted. In the conjugated state, the molecule is colored or isred-shifted.

For the molecules in Example 1b, a single monolayer molecular film isgrown, for example using Langmuir-Blodgett techniques or self-assembledmonolayers, such that the orientation axis of the molecules isperpendicular to the plane of the electrodes used to switch themolecules. Electrodes may be deposited in the manner described byCollier et al, supra, or methods described in the above-referencedpatent applications and issued patent. Alternate thicker film depositiontechniques include vapor phase deposition, contact or ink-jet printing,or silk screening.

Example 2a below depicts a second generic molecular example for thisModel 1.

where:

The letter A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

The letter D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), or substitutedhydrocarbon or functional group with at least one of hetero atom (e.g.,B, Si, I, N, O, S, P). The donor is differentiated from the acceptor bythat fact that it is less electronegative, or more electropositive, thanthe acceptor group on the molecule.

The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

The letters SA and SB are used here to designate Stator A and Stator B.They can be a hydrocarbon (either unsaturated or saturated) orsubstituted hydrocarbon. Typically, these hydrocarbon units containconjugated rings that contribute to the extended conjugation of themolecule when it is in a planar state (red shifted state). In thosestator units, they may contain bridging groups G_(n) and/or spacinggroups R_(n). A bridging group is typically used to connect the statorand rotor or to connect two or more conjugated rings to achieve adesired chromophore The connector may alternately comprise a single atombridge, such as an ether bridge with an oxygen atom, or a direct sigmabond between the rotor and stator. A spacing group provides anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor.

Example 2b below is another real molecular example of Model 1.

where:

The letter A⁻ is an Acceptor group; it is an electron-withdrawing group.It may be one of following: hydrogen, carboxylic acid or itsderivatives, sulfuric acid or its derivatives, phosphoric acid or itsderivatives, nitro, nitrile, hetero atoms (e.g., N, O, S, P, F, Cl, Br),or functional group with at least one of above-mentioned hetero atoms(e.g., OH, SH, NH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

The letter D⁺ represents a Donor group; it is an electron-donatinggroup. It may be one of following: hydrogen, amine, OH, SH, ether,hydrocarbon (either saturated or unsaturated), or substitutedhydrocarbon or functional group with at least one of hetero atom (e.g.,B, Si, I, N, O, S, P). The donor is differentiated from the acceptor bythat fact that it is less electronegative, or more electropositive, thanthe acceptor group on the molecule.

The letters Con₁ and Con₂ represent connecting units between onemolecule and another molecule or between a molecule and the solidsubstrate (e.g., metal electrode, inorganic or organic substrate, etc.).They may be any one of the following: hydrogen (utilizing a hydrogenbond), multivalent hetero atoms (i.e., C, N, O, S, P, etc.) orfunctional groups containing these hetero atoms (e.g., NH, PH, etc.),hydrocarbons (either saturated or unsaturated) or substitutedhydrocarbons.

The letters R₁, R₂ and R₃ represent spacing groups built into themolecule. The function of these spacer units is to provide anappropriate 3-dimensional scaffolding to allow the molecules to packtogether while providing rotational space for each rotor. They may beany one of the following: hydrogen, hydrocarbon (either saturated orunsaturated) or substituted hydrocarbon.

The letters G₁, G₂, G₃, G₄, G₅, G₆, G₇, and G₈ are bridging groups. Thefunction of these bridging groups is to connect the stator and rotor orto connect two or more conjugated rings to achieve a desiredchromophore. They may be any one of the following: hetero atoms (e.g.,C, N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH or NHNH, etc.), hydrocarbons(either saturated or unsaturated) or substituted hydrocarbons. Theconnector may alternately comprise a single atom bridge such as an etherbridge with an oxygen atom, or a direct sigma bond between the rotor andstator.

The letters J₁ and J₂ represent tuning groups built into the molecule.The function of these tuning groups (e.g., OH, NHR, COOH, CN, nitro,etc.) is to provide an appropriate functional effect (e.g. bothinductive effect and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO/LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecular conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g. hydrogen bonding, Coulomb interaction, van der Waals forces) or toprovide bi- or multiple-stability of molecular orientations. They may beany one of the following: hydrogen, hetero atoms (e.g., N, O, S, P, B,F, Cl, Br, and I), functional groups with at least one ofabove-mentioned hetero atoms, hydrocarbons (either saturated orunsaturated) or substituted hydrocarbons.

The molecule shown above (Example 2b) has been designed with theinternal rotor parallel to the orientation axis of the entire molecule.In this case, the external field is applied perpendicular to themolecular axis—the electrodes are oriented parallel to the long axis ofthe molecule and can be either nominally perpendicular or parallel tothe plane of the above model structures. For example, application of anelectric field to the upper molecule shown above where the field linesare perpendicular to the molecular axis and pointing upward will causethe rotor as pictured in that diagram to rotate to approximately 90degrees and appear edge on, as shown in the lower molecular diagramabove, and vice versa. In this case, the rotor as pictured in the lowerdiagram is not coplanar with the rest of the molecule, so this is theblue-shifted optical state of the molecule, or optical state II, whereasthe rotor is coplanar with the rest of the molecule on the upperdiagram, so this is the red-shifted optical state of the molecule, oroptical state I. The letters N, H, and O retain their usual meaning.).

FIG. 5 a depicts molecules similar to those of Examples 1b and 2b, butsimpler, comprising a middle rotor portion 432 and two end statorportions 434. As in Examples 1b and 2b, the rotor portion 432 comprisesa benzene ring that is provided with substituents that render the rotorwith a dipole. The two stator portions 434 are each covalently bonded tothe benzene ring through an azo linkage, and both portions comprise anaromatic ring.

FIG. 5 b is a schematic representation (perspective), illustrating theplanar state, with the rotor 432 and stators 434 all co-planar. In theplanar state, the molecule 430 is fully conjugated, evidences color(first spectral or optical state), and is comparatively moreelectrically conductive. The conjugation of the rings is illustrated bythe π-orbital clouds 500 a, 500 b above and below, respectively, theplane of the molecule 430.

FIG. 5 c is also a schematic representation (perspective), illustratingthe rotated state, with the rotor 432 rotated 90° with respect to thestators 434, which remain coplanar. In the rotated state, theconjugation of the molecule 430 is broken. Consequently, the molecule430 is transparent (second spectral or optical state) and comparativelyless electrically conductive.

For the molecules of Example 2b, the films are constructed such that themolecular axis is parallel to the plane of the electrodes. This mayinvolve films that are multiple monolayers thick. The molecules formsolid-state or liquid crystals in which the large stator groups arelocked into position by intermolecular interactions or direct bonding toa support structure, but the rotor is small enough to move within thelattice of the molecules. This type of structure can be used to build anE-field controlled display or used for other applications as mentionedearlier herein.

Model (2a): E-Field Induced Band Gap Change Caused by the Change ofExtended Conjugation Via Charge Separation or Recombination Accompaniedby Increasing or Decreasing Band Localization

FIG. 6 a is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via charge separation or recombination accompanied byincreasing or decreasing band localization. As shown in FIG. 6 a, themolecule 630 comprises two portions 632 and 634. The molecule 630evidences a larger band gap state, with less π-delocalization.Application of an electric field causes charge separation in themolecule 630, resulting in a smaller band gap state, with betterπ-delocalization. Recombination of the charges returns the molecule 630to its original state.

The following requirements must be met in this model:

(a) The molecule must have a modest dielectric constant ∈_(r) and can beeasily polarized by an external E-field, with ∈_(r) in the range of 2 to10 and polarization fields ranging from 0.01 to 10 V/nm;

(b) At least one segment of the molecule must have non-bondingelectrons, or π-electrons, or π-electrons and non-bonding electrons thatcan be mobilized over the entire molecule or a part of the molecule;

(c) The molecule can be symmetrical or asymmetrical;

(d) The inducible dipole(s) of the molecule can be oriented in at leastone direction;

(e) The charges will be separated either partially or completely duringE-field induced polarization;

(f) The states of charge separation or recombination can be E-fielddependent or bi-stable, stabilized through inter- or intra-molecularforces such as covalent bond formation, hydrogen bonding, chargeattraction, Coulomb forces, metal complex, or Lewis acid (base) complex,etc.;

(g) The process of charge separation or recombination of the moleculecan involve or not involve σ- and π-breakage or formation; and

(h) During the charge separation or re-combination process activated byan E-field, the band gap of the molecule will change depending on thedegree of the non-bonding electron, or π-electron, or π-electron andnon-bonding electron delocalization in the molecule. Both optical andelectrical properties of the molecules will be changed accordingly.

One example of an E-field induced band gap change (color change) viacharge separation or recombination involving bond breaking or bondformation is shown below (Example 3):

where:

The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is to provide an appropriate functional effect (e.g., bothinductive effect and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO/LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecule conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g., hydrogen bonding, Coulomb interaction, van der Waals forces) toprovide bi- or multiple-stability of molecular orientation. They may beany one of the following: hydrogen, hetero atom (e.g., N, O, S, P, B, F,Cl, Br and I), functional group with at least one of above-mentionedhetero atoms, hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

The letter G₁ is a bridging group. The function of the bridging group isto connect two or more conjugated rings to achieve a desiredchromophore. The bridging group may be any one of the following: heteroatoms (e.g., N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH, etc.), hydrocarbon orsubstituted hydrocarbon.

The letter W is an electron-withdrawing group. The function of thisgroup is to tune the reactivity of the maleic anhydride group of thismolecule, which enables the molecule to undergo a smooth chargeseparation or recombination (bond breaking or formation, etc.) under theinfluence of an applied external E-field. The electron-withdrawing groupmay be any one of the following: carboxylic acid or its derivatives(e.g., ester or amide etc.), nitro, nitrile, ketone, aldehyde, sulfone,sulfuric acid or its derivatives, hetero atoms (e.g., F, Cl, etc.) orfunctional group with at least one of the hetero atoms (e.g., F, Cl, Br,N, O, S, etc.).

An example of an E-field induced band gap change involving the formationof a molecule-metal complex or a molecule-Lewis acid complex is shownbelow (Example 4):

where:

The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is to provide an appropriate functional effect (e.g. bothinductive and resonance effects) and/or steric effects. The functionaleffect is to tune the band gap (ΔE_(HOMO/LUMO)) of the molecule to getthe desired electronic as well as optical properties of the molecule.The steric effect is to tune the molecular conformation through sterichindrance, inter- or intra-molecular interaction forces (e.g., hydrogenbonding, Coulomb interaction, van der Waals forces) to provide bi- ormultiple-stability of the molecular orientation. They may be any one ofthe following: hydrogen, hetero atom (e.g., N, O, S, P, B, F, Cl, Br,and I), functional group with at least one of the above-mentioned heteroatoms, hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

The letter G₁ is a bridging group. The function of the bridging group isto connect two or more conjugated rings to achieve a desiredchromophore. The bridging group may be any one of the following: heteroatoms (e.g., N, O, S, P, etc.) or functional group with at least one ofabove-mentioned hetero atoms (e.g., NH, etc.) or substitutedhydrocarbon.

M⁺ represents metals, including transition metals, or their halogencomplexes or H⁺ or other type of Lewis acid(s).

Model (2b): E-Field Induced Band Gap Change Caused by the Change ofExtended Conjugation via Charge Separation or Recombination and π-BondBreaking or Formation

FIG. 6 b is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via charge separation or recombination and π-bond breakingor formation. As shown in FIG. 6 b, the molecule 630′ comprises twoportions 632′ and 634′. The molecule 630′ evidences a smaller band gapstate. Application of an electric field causes breaking of the π-bond inthe molecule 630′, resulting in a larger band gap state. Reversal of theE-field re-connects the π-bond between the two portions 632′ and 634′and returns the molecule 630′ to its original state.

The requirements that must be met in this model are the same as listedfor Model 2(a).

One example of an E-field induced band gap change cause by extendedconjugation via charge separation (σ-bond breaking and π-bond formation)is shown below (Example 5):

where:

The letter Q is used here to designate a connecting unit between twophenyl rings. It can be any one of following: S, O, NH, NR, hydrocarbon,or substituted hydrocarbon.

The letters Con₁ and Con₂ are connecting groups between one molecule andanother molecule or between a molecule and a solid substrate (e.g.,metal electrode, inorganic or organic substrate, etc.). They may be anyone of the following: hydrogen (through a hydrogen bond), hetero atoms(i.e., N, O, S, P, etc.) or functional groups with at least one ofabove-mentioned hetero atoms (e.g., NH, etc.), hydrocarbons (eithersaturated or unsaturated) or substituted hydrocarbons.

The letters R₁ and R₂ represent spacing groups built into the molecule.The function of these spacer units is to provide an appropriate3-dimensional scaffolding to allow the molecules to pack together whileproviding rotational space for each rotor. They may be any one of thefollowing: hydrogen, hydrocarbons (either saturated or unsaturated) orsubstituted hydrocarbons.

The letters J₁, J₂, J₃ and J₄ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is to provide an appropriate functional effect (e.g. bothinductive and resonance effects) and/or steric effects. The functionaleffect is to tune the band gap (ΔE_(HOMO/LUMO)) of the molecule to getthe desired electronic as well as optical properties of the molecule.The steric effect is to tune the molecular conformation through sterichindrance, inter- or intra-molecular interaction forces (e.g., hydrogenbonding, Coulomb interaction, van der Waals forces) to provide bi- ormultiple-stability of molecular orientation. They may also be used asspacing group to provide an appropriate 3-dimensional scaffolding toallow the molecules to pack together while providing rotational spacefor each rotor. They may be any one of the following: hydrogen, heteroatom (e.g., N, O, S, P, B, F, Cl, Br, and I), functional group with atleast one of above-mentioned hetero atom, hydrocarbon (either saturatedor unsaturated) or substituted hydrocarbon.

The letter G₁ is a bridging group. The function of the bridging group isto connect the stator and rotor or to connect two or more conjugatedrings to achieve a desired chromophore. The bridging group may be anyone of the following: hetero atoms (e.g., N, O, S, P, etc.) orfunctional groups with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

The letter W is an electron-withdrawing group. The function of thisgroup is to tune the reactivity of the lactone group of this molecule,which enables the molecule to undergo a smooth charge separation orrecombination (bond breaking or formation, etc.) under the influence ofan applied external E-field. The electron-withdrawing group may be anyone of the following: carboxylic acid or its derivatives (e.g., ester oramide etc.), nitro, nitrile, ketone, aldehyde, sulfone, sulfuric acid orits derivatives, hetero atoms (e.g., F, Cl, etc.) or functional groupwith at least one of hetero atoms (e.g., F, Cl, Br, N, O and S, etc.),hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

The uppermost molecular structure has a smaller band gap state than thelowermost molecular structure.

Another example of an E-field induced band gap change caused by breakageof extended π-bond conjugation via charge recombination and σ-bondformation is shown below (Example 6):

where:

The letter Q is used here to designate a connecting unit between twophenyl rings. It can be any one of following: S, O, NH, NR, hydrocarbon,or substituted hydrocarbon.

The letters Con₁ and Con₂ are connecting groups between one molecule andanother molecule or between a molecule and a solid substrate (e.g.,metal electrode, inorganic or organic substrate, etc.). They may be anyone of the following: hydrogen, hetero atoms (i.e., N, O, S, P, etc.) orfunctional group with at least one of above-mentioned hetero atoms(e.g., NH, etc.), hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

The letters R₁ and R₂ represent spacing groups built into the molecule.The function of these spacer units is to provide an appropriate3-dimensional scaffolding to allow the molecules to pack together whileproviding rotational space for each rotor. They may be any one of thefollowing: hydrogen, hydrocarbon (either saturated or unsaturated) orsubstituted hydrocarbon.

The letters J₁, J₂, J₃ and J₄ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is to provide an appropriate functional effect (e.g., bothinductive and resonance effects) and/or steric effects. The functionaleffect is to tune the band gap (ΔE_(HOMO/LUMO)) of the molecule to getthe desired electronic as well as optical properties of the molecule.The steric effect is to tune the molecule conformation through sterichindrance, inter- or intra-molecular interaction forces (e.g. hydrogenbonding, Coulomb interaction, van der Waals forces) to provide bi- ormultiple-stability of molecular orientation. They may also be used asspacing groups to provide an appropriate 3-dimensional scaffolding toallow the molecules to pack together while providing rotational spacefor each rotor. They may be any one of the following: hydrogen, heteroatom (e.g., N, O, S, P, B, F, Cl, Br, and I), functional groups with atleast one of above-mentioned hetero atom, hydrocarbon (either saturatedor unsaturated) or substituted hydrocarbon.

The letter G₁ is a bridging group. The function of this bridging groupis to connect stator and rotor or to connect two or more conjugatedrings to achieve a desired chromophore. The bridging group may be anyone of the following: hetero atoms (e.g., N, O, S, P, etc.) orfunctional group with at least one of above-mentioned hetero atoms(e.g., NH or NHNH, etc.), hydrocarbon (either saturated or unsaturated)or substituted hydrocarbon.

The letter W is an electron-withdrawing group. The function of thisgroup is to tune the reactivity of the lactone group of this molecule,which enables the molecule to undergo a smooth charge separation orrecombination (bond breaking or formation, etc.) under the influence ofan applied external E-field. The electron-withdrawing group may be anyone of the following: carboxylic acid or its derivatives (e.g., ester oramide, etc.), nitro, nitrile, ketone, aldehyde, sulfone, sulfuric acidor its derivatives, hetero atoms (e.g., F, Cl etc.) or functional groupwith at least one of hetero atoms (e.g., F, Cl, Br, N, O, S, etc.),hydrocarbon (either saturated or unsaturated) or substitutedhydrocarbon.

Again, the uppermost molecular structure has a smaller band gap statethan the lowermost molecular structure.

The present invention turns ink or dye molecules into active devicesthat can be switched with an external electric field by a mechanismcompletely different from any previously described electro-chromic orchromogenic material. The general idea is to use modified Crystal Violetlactone type of molecules in which the C—O bond of the lactone issufficiently labile enough and can undergo a bond breaking and forming(see Examples 5 and 6 above) under the influence of an applied electricfield.

A positive and a negative charge are generated during the C—O bondbreaking process. The resulting charges will be separated and move inopposite directions parallel to the applied external field (upper partof the molecule), or bond rotation (lower part of the molecule. The twoaromatic rings with an extended dipole (upper part and lower part) ofthe molecule is completely conjugated, and a color (red-shift) results(see Example 5). However, the molecule is designed to have inter- and/orintra-molecular forces, such as hydrogen bonding, Coulomb, ordipole-dipole interactions as well as steric repulsions, or by apermanent external E-field to stabilize both charges in this particularorientation. Thus, a large field is required to unlatch the moleculefrom its initial orientation. Once switched into a particularorientation, the molecule will remain in that orientation until it isswitched out.

When a reverse E-field is applied (Example 6), both charges tend torealign themselves to the direction of the reverse external field. Thepositive charge on the upper part of the molecule will migrate to thecenter part of the molecule (tri-aryl methane position) from the side ofthe molecule through the non-bonding electron, or π-electron, orπ-electron and non-bonding electron delocalization. Likewise, thenegative charged lower part of the molecule will tend to move closer tothe external E-field through C—C bond rotation. A key component of themolecule design is that there is a steric and static repulsion betweenthe CO₂ ⁻ and the J₃ and J₄ groups that will prevent the lower part ofthe molecule (the negative charged sector) from rotating through acomplete 180 degree half cycle. Instead, the rotation is halted by thesteric interaction of bulky groups on the lower part and the upper partat an angle of approximately 90 degrees from the initial orientation.Furthermore, this 90 degree orientation is stabilized by a C—O bondformation and charge recombination. During this process, a tetrahedralcarbon (an isolator) is formed at the tri-aryl methane position. Theconjugation of the molecule is broken and the HOMO and LUMO are nolonger delocalized over the entire upper part of the molecule. This hasthe effect of shrinking the size of the volume occupied by theelectrons, which causes the HOMO-LUMO gap to increase. A blue-shiftedcolor or transparent state will result during this process.

For colored ink and dye molecules, the limitation of the positive chargemigration just between one side of a molecule and the center position iscrucial. Another important factor is the ability to switch the rotor(lower part of molecule) between two states separated by an opticallysignificant angle (nominally 10 to 170 degrees) from the stators (theupper part of the molecule). When the intra-molecular charge separationreaches a maximum distance, then the upper most part of the moleculebecomes completely conjugated. Thus, the π-electrons or π-electrons andnon-bonding electrons of the molecule, through its highest occupiedmolecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO),are delocalized over the upper most region. The effect is identical tothat for a quantum mechanical particle in a box: when the box is thesize of the entire molecule, i.e., when the orbitals are delocalized,then the gap between the HOMO and LUMO is relatively small. In thiscase, the HOMO-LUMO gap of the molecule is designed to yield the desiredcolor of the ink or dye. The HOMO-LUMO gap for the all-parallelstructure can be tuned by substituting various chemical groups (J₁, J₂,J₃, J₄, and W) onto the different aromatic rings of the molecule. In thecase where the rotor (lower part of the molecule) is rotated by 10 to170 degrees with respect to the stators (the upper part of themolecule), depending on the nature of the chemical substituents (J₁, J₂,J₃, J₄, and W) bonded to the rotor and stator, then the increasedHOMO-LUMO gap will correspond to a color that is blue-shifted withrespect to the color of the all-parallel structure. With sufficientshifting, the molecule becomes transparent, if the new HOMO-LUMO gap islarge enough. Thus, the molecule is switchable between two colors orfrom one color to a transparent state.

Examples 5 and 6 show two different states of a representativeswitchable molecule under the influence of an externally appliedE-field. For this particular type of molecule, a sufficiently thickmolecular film is grown, for example using Langmuir-Blodgett techniques,vapor phase deposition, or electrochemical deposition, such that theorientation axis of the molecules is perpendicular to the plane of theelectrodes used to switch the molecules. Another deposition technique isto suspend the molecule as a monomer/oligomer or solvent-based solutionthat is thick film coated (e.g., reverse roll) or spin-coated onto thesubstrate and subsequently polymerized (e.g., by UV radiation) or driedwhile the coating is subjected to an electric field that orients themolecule. A top electrode may be a transparent conductor, such asindium-tin oxide, and the films are grown such that the molecular axisis parallel to the plane of the electrodes. The molecules formsolid-state or liquid crystals in which the large stator groups arelocked into position by intermolecular interactions or direct bonding toa support structure, but the rotor is small enough to move within thelattice of the molecules.

Model (3): E-Field Induced Band Gap Change via Molecular Folding orStretching

FIG. 7 is a schematic depiction of this model, which involves anE-field-induced band gap change caused by the change of extendedconjugation via molecular folding or stretching. As shown in FIG. 7, themolecule 730 comprises three portions 732, 734, and 736. The molecule730 evidences a smaller band gap state due to an extended conjugationthrough a large region of the molecule. Application of an electric fieldcauses breaking of the conjugation in the molecule 730, due to molecularfolding about the central portion 734, resulting in a larger band gapstate due to the non-extended conjugation in the large region of themolecule. Reversal of the E-field unfolds the molecule 730 and returnsthe molecule to its original state. Stretching and relaxing of thecentral portion 734 of the molecule 730 has the same effect.

The following requirements must be met in this Model:

(a) The molecule must have at least two segments;

(b) Several segments (portions) should have non-bonding electrons, orπ-electrons, or π-electrons and non-bonding electrons involved in theHOMOs, LUMOs, and nearby orbitals;

(c) The molecule may be either symmetrical or asymmetrical with a donorgroup on one side and an acceptor group on another side;

(d) At least two segments of the molecule have some functional groupsthat will help to stabilize both states of folding and stretchingthrough intra- or inter-molecular forces such as hydrogen bonding, vander Waals forces, Coulomb attraction or metal complex formation;

(e) The folding or stretching states of the molecule must be E-fieldaddressable;

(f) In at least one state (presumably in a fully stretched state), thenon-bonding electrons, or π-electrons, or π-electrons and non-bondingelectrons of the molecule will be well-delocalized, and the π- andp-electrons electrons of the molecule will be localized or onlypartially delocalized in other state(s);

(g) The band gap of the molecules will change depending on the degree ofnon-bonding electron, or π-electron, or π-electron and non-bondingelectron delocalization while the molecule is folded or stretched by anapplied external E-field, and this type of change will also affect theelectrical or optical properties of the molecule as well; and

(h) This characteristic can be applied to these types of molecules foroptical or electrical switches, gates, storage or display applications.

An example of an E-field induced band gap change via molecular foldingor stretching is shown below (Example 7):

where:

The letters R₁ and R₂ represent spacing groups built into the molecule.They may be any one of the following: hydrogen, hydrocarbon (eithersaturated or unsaturated) or substituted hydrocarbon.

The letters J₁, J₂, J₃, J₄ and J₅ represent tuning groups built into themolecule. The function of these tuning groups (e.g., OH, NHR, COOH, CN,nitro, etc.) is used to provide an appropriate functional effect (e.g.,both inductive and resonance effects) and/or steric effects. Thefunctional effect is to tune the band gap (ΔE_(HOMO/LUMO)) of themolecule to get the desired electronic as well as optical properties ofthe molecule. The steric effect is to tune the molecular conformationthrough steric hindrance, inter- or intra-molecular interaction forces(e.g. hydrogen bonding, Coulomb interaction, van der Waals forces) toprovide bi- or multiple-stability of molecular orientation. They mayalso be used as spacing group They may be any one of the following:hydrogen, hetero atom (e.g., N, O, S, P, B, F, Cl, Br and I), functionalgroup with at least one of above-mentioned hetero atom, hydrocarbon(either saturated or unsaturated) or substituted hydrocarbon.

Letters Y and Z are functional groups that will form inter- orintra-molecular hydrogen bonding. They may be any one of following: SH,OH, amine, hydrocarbon, or substituted hydrocarbon.

The molecule on the top of the graphic has a larger band gap due to thelocalized conjugation various parts of the molecule, while the moleculeon the bottom has a smaller band gap due to an extended conjugationthrough a large region of the molecule.

1. A method of fabricating rewritable media, the method comprising:providing a substrate; and forming with said substrate, a rewritablelayer wherein the writable-erasable layer is formed by a molecularsystem, said system including electrochromic switchable molecules, eachof said molecules being selectively switchable between at least twooptically distinguishable states.
 2. The method as set forth in claim 1,wherein said molecules exhibit an electric field induced band gapchange.
 3. The method as set forth in claim 2, wherein said electricfield induced band gap change occurs via a mechanism selected from agroup including (1) molecular conformation change or an isomerization,(2) change of extended conjugation via chemical bonding change to changethe band gap, and (3) molecular folding or stretching.
 4. The method asset forth in claim 2 wherein said electric field induced band gap changeoccurs via a molecular conformation change or an isomerization.
 5. Themethod as set forth in claim 4 wherein the molecules forming themolecular system include at least one stator portion and at least onerotor portion, wherein said rotor rotates from a first state to a secondstate with an applied electric field, wherein in said first state, thereis extended conjugation throughout said molecular system, resulting in arelatively smaller band gap, and wherein in said second state, saidextended conjugation is changed, resulting in a relatively larger bandgap.
 6. The method as set forth in claim 4 wherein, dependent upondirection of electrical field applied, in a first of said states saidmolecules are in a more conjugated state, having a relatively smallerband gap, and in a second of said states said colorant molecules are ina less conjugated state, having a relatively larger band gap.
 7. Themethod as set forth in 2 wherein said electric field induced band gapchange occurs via a change of extended conjugation via chemical bondingchange to change the band gap.
 8. The method as set forth in claim 7whersin said electric field induced band gap change occurs via a changeof extended conjugation via charge separation or recombinationaccompanied by increasing or decreasing band delocalization.
 9. Themethod as set forth in claim 8 wherein a change from a first state to asecond state occurs with an applied electric field, said changeinvolving charge separation in changing from said first state to saidsecond state, resulting in a relatively smaller band gap state, withgreater π-delocalization, and recombination of charge in changing fromsaid second state to said first state, resulting in a relatively lagerband gap state, with less π-delocalization.
 10. The method as set forthin claim 7 wherein said electric field induced band gap change occursvia a change of extended conjugation via charge separation orrecombination and π-bond breaking or formation.
 11. The method as setforth in claim 10 wherein a change from a first state to a second stateoccurs with an applied electric field, said change involving chargeseparation in changing from said first state to said second state,wherein in said first state there is no extended conjugation throughout,resulting in a relatively larger band gap state, and wherein in saidsecond state said extended conjugation is formed and separated positiveand negative charges are created, resulting in a relatively smaller bandgap state.
 12. The method as set forth in claim 2 wherein said electricfield induced band gap change occurs via a molecular folding orstretching.
 13. The method as set forth in claim 12 wherein saidcolorant has three portions, a first portion and a third portion, eachbonded to a second, central portion, wherein a change from a first stateto a second state occurs with an applied electric field, said changeinvolving a folding or stretching about of said second portion, whereinin said first state there is extended conjugation, resulting in arelatively smaller band gap state, and wherein in said second state,said extended conjugation is chanced, resulting in a relatively largerband gap.
 14. The method as set forth in claim 1 wherein said moleculesare bistable, providing a non-volatile component.
 15. The method as setforth in claim 1 wherein said molecules have a low activation barrierbetween different said states providing a fast volatile switch.
 16. Themethod colorant as set forth in claim 1 wherein said molecules have morethan two said states, switchable such that optical properties can betuned either continuously by application of a decreasing or increasingelectric field to form a volatile switch or color of selectedcomposition regions is changed abruptly by application of voltage pulsesto switch with at least one molecular activation barrier.
 17. A methodof doing business of fabricating rewritable media, the methodcomprising: receiving a flexible material substrate; and forming uponsaid substrate at least one rewritable layer wherein the layer is formedby a molecular system, said system including electrochromic switchablemolecules, each of said molecules being selectively switchable betweenat least two optically distinguishable states.
 18. The method as setforth in claim 17 wherein said layer is a molecular colorant coatingwherein molecules of the coating are at least bichromal and subject tobistable switching between two electro-optical states under influence ofa localized electrical field via band gap changes.
 19. The method as setforth in claim 18 wherein said band gap changes occur via a mechanismselected from a group including (1) molecular conformational change oran isomenzation, (2) change of extended conjugation via chemical bondingchange to change the band gap, and (3) molecular folding or stretching.20. The method as set forth in claim 17 wherein said molecules arebistable, providing a non-volatile component.
 21. The method as setforth in claim 17 wherein said molecules have a low activation barrierbetween different said states providing a fast volatile switch.
 22. Themethod as set forth in claim 17 wherein selected molecules switchbetween a transparent state and a colored state.
 23. The method as setforth in claim 17 wherein said substrate is configured for switchingselected bit elements of said substrate formed by said molecules betweentwo visually distinctive color states.
 24. The method as set forth inclaim 17 wherein said substrate is configured for switching pictureelements formed by said molecules between a transparent state and acolor state.
 25. The method as set forth in claim 17 wherein saidmolecules switch between one index of refraction and another index ofrefraction.
 26. The method as set forth in claim 17 wherein saidmolecules are bistable.
 27. The method as set forth in claim 17 whereinsaid molecules are bimodal.
 28. The method as set forth in claim 17wherein said molecules are arranged to form discrete, addressablepicture elements of a surface of said substrate.
 29. The method as setforth in claim 17 wherein said molecules are selectively switchablebetween a transparent state and an opaque state and are distributedacross said substrate as an overlay for forming picture elementsthereon.
 30. The method as set forth in claim 17 wherein pictureelements of the substrate consist of a mosaic pattern of said moleculeswherein said pattern has optically combinable visual color states. 31.The method as set forth in claim 17 wherein said picture elements of thesubstrate consist of a mosaic pattern of said molecules wherein saidpattern forms a mosaic of primary colors.
 32. The method as set forth inclaim 17 wherein said molecules are selectively switchable between atransparent state and an opaque state and are distributed across saidsubstrate as an overlay of a mosaic pattern of primary color subpixelregions.
 33. The method as set forth in calim 17 where the layer is acolorant is printed on a white substrate for passive light viewing. 34.The method as set forth in claim 17 wherein the layer is a colorant isprinted on a transparent substrate for overhead projection use.